Physical channel segmentation in wireless communication system

ABSTRACT

A wireless communication transmitter ( 200 ) configured to segment a transport block into C segments, encode each segment into a set of encoded bits, determine, for γ encoded segments, a subset of size M 0 ′ of encoded bits for each encoded segment and for C−γ encoded segments, a subset of size M 1 ′ of encoded bits for each encoded segment, wherein the subset sizes M 0 ′ and M 1 ′ differ at most by P bits, where P is a product of a modulation order and a number of transmission layers over which the transport block is transmitted. The selected subsets of encoded bits are concatenated and grouped to form modulation symbols of the modulation order.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to wireless communications andmore particularly to physical channel segmentation in wirelesscommunication systems and corresponding methods.

BACKGROUND

The physical layer of some wireless communication systems using forwarderror correction (FEC) coding must be able to transmit a wide variety ofpacket sizes. In order to bound the memory usage of the FEC decoder insuch systems, it is known to break up or “segment” larger informationpackets into smaller “code block segments”, which are encodedindependently. When segmentation is used, there is a need for rules thatdetermine the number of physical channel resources to assign to eachcode block segment. These rules are referred to here as “physicalchannel segmentation” rules.

In the High Speed Packet Access (HSPA) extension of the 3GPP UniversalMobile Telecommunications System (UMTS) protocol, the physical channelsegmentation rule is applied after a step of concatenating all of theencoded code block segments. Therefore, the segmented physical channelresources are not directly identifiable with code block segments. Thisadversely affects the ability to pipeline the channel equalization andchannel decoding in the receiver.

In the WiMAX protocol, the segmented physical channel resources aredirectly identifiable with code block segments. However, in WiMAX, thephysical channel resources can be segmented to a granularity of 48modulation symbols, and all code block segments must have exactly thesame code rate. In systems like the developing Long Term Evolution (LTE)of the 3GPP UMTS protocol where the available physical channel resourceschange from frame-to-frame, a much more flexible solution with a finergranularity of segmented physical channel resources is required.

The various aspects, features and advantages of the present disclosurewill become more fully apparent to those having ordinary skill in theart upon careful consideration of the following Detailed Descriptionthereof with the accompanying drawings described below. The drawings mayhave been simplified for clarity and are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative wireless communication system.

FIG. 2 is a block diagram of an exemplary wireless communication systemtransmitter.

FIG. 3 is a block diagram of an exemplary wireless communicationreceiver.

FIG. 4 is a wireless communication receiver for serially orientedsegmentation processing.

DETAILED DESCRIPTION

In FIG. 1, a wireless communication system 100 comprises one or morefixed base infrastructure units forming a network distributed over ageographical region. The base unit may also be referred to as an accesspoint, access terminal, Node-B, eNode-B or by other terminology used inthe art. In FIG. 1, the one or more base units 101 and 102 serve anumber of remote units 103 and 110 within a serving area, for example, acell or a cell sector. The remote units may be fixed units or mobileterminals. The remote units may also be referred to as subscriber units,mobile stations, users, terminals, subscriber stations, user equipment(UE), terminals, or by other terminology used in the art. The instantdisclosure however is not to be limited to any particular wirelesscommunication system architecture.

Generally, the base units 101 and 102 transmit downlink communicationsignals 104 and 105 to serve remote units in the time and/or frequencydomain. The remote units 103 and 110 communicate with the one or morebase units via uplink communication signals 106 and 113. The one or morebase units may comprise one or more transmitters and one or morereceivers for downlink and uplink transmissions. The remote units mayalso comprise one or more transmitters and one or more receivers.

In one implementation, the wireless communication system is compliantwith the developing Long Term Evolution (LTE) of the 3GPP UniversalMobile Telecommunications System (UMTS) protocol wherein the basestation transmits using an orthogonal frequency division multiplexing(OFDM) modulation scheme on the downlink and the user terminals transmiton the uplink using a single carrier frequency division multiple access(SC-FDMA) scheme. More generally, however, the wireless communicationsystem may implement some other open or proprietary communicationprotocol. The present disclosure is not intended to be limited to theimplementation of any particular communication protocol.

In some system implementations using forward error correction (FEC)coding, the physical layer must be able to transmit a wide variety ofpacket sizes. In some systems, large information packets are divided orbroken into smaller “code block segments” which may be encodedindependently. The purpose of this is generally to bound the memoryusage of the FEC decoder. Additionally, identifying a distinct set ofphysical channel resources for each code block segment facilitatespipelining of the channel equalization and FEC decoding in the receiver.Determining the number of physical channel resources to allot to eachcode block segment is referred to here as “physical channelsegmentation.” Assuming the same modulation order is applied to all codeblock segments, physical channel segmentation is equivalent todetermining the number of encoded bits from each code block segment totransmit over the channel.

FIG. 2 illustrates a wireless transmitter 200, which may be implementedas an infrastructure entity and/or a wireless terminal, for example, amobile or fixed base subscriber. In FIG. 2, a K-bit information packet,or transport block, enters the transmitter for transmission over achannel. A segmenting entity 202 is configured to segment the transportblock into segments. In one implementation, the segmenting entity isconfigured to segment the transport block such that at least twosegments contain a common number of bits. More generally, the K-bitpacket is segmented into C code block segments, where the i-th segmentcontains K_(i) information bits, 0≦i<C, and

$\begin{matrix}{K = {\sum\limits_{i = 0}^{C - 1}{K_{i}.}}} & (1)\end{matrix}$

In FIG. 2, before channel encoding, in some embodiments, a paddingentity 204 inserts a small number of bits, other than those in theinformation packet, into each code block segment. The bits may beinserted by pre-pending or by appending. For example, a code blocksegment may be padded by inserting 0's (called “zero padding”) or byinserting some other pre-determined bit sequence so that the segment maybe handled by the channel encoder. In another example, the paddingentity attaches cyclic redundancy check (CRC) parity bits to eachindividual code block segment to provide error detection. Regardless ofthe types of bits inserted, the segment is regarded as being a paddedcode block segment or a padded sequence. Not all transmitterimplementations include bit padding.

In FIG. 2, an encoding entity is configured to encode each segment intoa set of encoded bits. After individually encoding the padded code blocksegments, a rate matching entity 208 individually rate matches theencoded bits for each segment to select subsets of the encoded bits totransmit over the channel.

In FIG. 2, a total of N complex modulation symbols are available totransmit the information packet over the channel, where each modulationsymbol is selected by a group of Q encoded bits. For instance, Q=2, 4,or 6 for QPSK, 16-QAM, or 64-QAM modulation, respectively. Thus, a totalof QN encoded bits may be transmitted over the channel. A physicalchannel segmentation rule determines the number M_(i) of encoded bitsfor the i-th code block segment, 0≦i<C, to transmit over the channelsuch that

$\begin{matrix}{{Q\; N} = {\sum\limits_{i = 0}^{C - 1}{M_{i}.}}} & (2)\end{matrix}$

In some embodiments of FIG. 2 there may be only two distinct sizes ofthe M_(i) encoded bits, 0≦i<C. For instance, for γ segments we may haveM₀=M₁= . . . =M_(γ−1)=M₀′, and for the remaining C-γ segments we mayhave M_(γ)=M_(γ+1)= . . . =M_(C-1)=M₁′. Further, in some embodiments thedifference between M₀′ and M₁′ may be either Q or the product of Q and athe number of transmission layers over which the packet is transmitted.

In FIG. 2, a concatenating entity 210 is configured to concatenate theselected subsets of encoded bits after rate matching. The transmitteralso includes a grouping entity configured to group the concatenatedselected subsets of encoded bits in order to form modulation symbols ofthe modulation order and a transmitter entity 212 configured to transmitthe modulation symbols, possibly making use of multiple transmitantennas. When multiple transmit antennas are used, multipletransmission layers may also be used to transmit the packet. The numberof transmission layers is the effective number of non-redundantmodulation symbols transmitted on the same time-frequency resourceacross multiple antennas. The number of layers over which the packet istransmitted must be less than or equal to the number of antennas overwhich the packet is transmitted.

Although FIG. 2 illustrates C padding, encoding, and rate matchingsteps, the illustration should not be construed as implying that theseprocessing steps must occur in parallel. Alternatively, these steps,which are applied on a code block-by-code block basis, can be performedserially, one code block at a time.

FIG. 3 illustrates a wireless receiver 300 capable of processing asignal transmitted by the transmitter of FIG. 2. The receiver includes anumber of antennas for receiving the signal and a demodulator entity 304for demodulating the signal, which is demodulated to produce QNlog-likelihood ratios (LLRs) for the received packet. The log-likelihoodratio of a bit b, LLR_(b), may be defined as

$\begin{matrix}{{L\; L\; R_{b}} = {\log\frac{p\left( {\left. \underset{\_}{r} \middle| b \right. = 1} \right)}{p\left( {\left. \underset{\_}{r} \middle| b \right. = 0} \right)}}} & (3)\end{matrix}$

where b is one of the Q bits used to select the transmitted complexmodulation symbol, r is the received complex modulation symbol, p(r|b=1)is the probability of receiving r given that b is 1, and p(r|b=0) is theprobability of receiving r given that b is 0. Obeying the same physicalchannel segmentation rule used in the transmitter, the receiver includesa segmentation entity 306 that divides the QN LLRs into C segments,where the i-th segment, 0≦i<C, contains M_(i) LLRs. The C code blocksegments are each de-rate matched, decoded, and de-padded by a de-ratematching entity 308, a decoding entity 310 and a de-padding entity 312,respectively, to generate the received information bits, where the i-thsegment, 0≦i<C, contains K_(i) bits. Thereafter, a concatenating entity314 concatenates the segments.

FIG. 3 should not be construed as implying that the C de-rate matching,decoding, and de-padding steps must occur in parallel. FEC decoders, forexample turbo decoders, often require large amounts of memory to storeintermediate results, and the required memory size is proportional tothe maximum code block size. Therefore, in some receiver embodiments,the de-rate matching, decoding, and de-padding steps are applied to thecode block segments serially, one code block at a time.

The description above identifies two segmentation rules in acommunication system. A code block segmentation rule is disclosed thatdetermines the C segment sizes K_(i) such that Equation (1) issatisfied. A physical channel segmentation rule is disclosed thatdivides the QN encoded bits available to transmit the packet into Csegment sizes M_(i) such that Equation (2) is satisfied. Assuming agiven code block segmentation rule, this document addresses only thephysical channel segmentation rule, two possibilities for which arepresented below.

FIG. 4 is a wireless communication receiver 400 for serially orientedsegmentation processing. The receiver stores the N received complexmodulation symbols for the information packet in a buffer 402, whichtypically is a random access memory (RAM). The code block segments areprocessed serially, i.e., one at a time, by first fetching the receivedsymbols for the code block segment from the buffer and equalizing thefetched symbols at 404 to compensate for channel effects. LLRs aregenerated at 406 for all the bits of the received symbols. The generatedLLRs are de-rate matched at 408, decoded at 410, and de-padded at 412,and the decoded information bits are appended to an output buffer 414.After the C code block segments have been so processed, the outputbuffer will contain the K received bits for the information packet.

A constraint that simplifies the receiver implementation of FIG. 4 is torequire that the encoded bits of each code block occupy an integernumber of modulation symbols. Symbolically, this requirement isequivalent toM _(i) ∝Q  (4)

for all i, 0≦i<C. This constraint allows the equalizer to read aninteger number of modulation symbols from the symbol buffer, generateLLRs for all bits of the symbols, and pass all generated LLRs directlyto the decoder. Since there is no possibility that a modulation symbolwould contain encoded bits from two different code block segments, thereis no need for special handling procedures by the equalizer.

When multiple antennas are used at the transmitter, the particularsignaling used might require the equalizer to fetch and compensate forchannel effects over more than one received symbol. For instance,consider Alamouti-style space-time block coding with two transmitantennas and two receive antennas. In this transmission technique, thetransmitter space-time encodes two symbols at a time, i.e., four channeluses are used to transmit two symbols, and hence the equalizer of FIG. 4must fetch and process two received symbols (in addition to tworedundant symbols) at a time to compensate for channel effects. In thisexample, the number of transmission layers is also two. A result of thisequalization processes may be that all LLRs for two modulation symbolsare generated in parallel. In this case, to eliminate the possibilitythat the LLRs generated in parallel contain encoded bits for differentcode block segments, thereby simplifying the equalizer design, it isnecessary to require that the code block segments contain an even numberof modulation symbols. Multiple-input multiple-output (MIMO)transmission presents similar cases where the receiver equalizes andgenerates all LLRs for multiple symbols in parallel.

In general, let the number of symbols the equalizer must process inparallel be an integer L. Then the equalizer design can be simplified byrequiring

$\begin{matrix}{\frac{M_{i}}{Q} \propto L} & (5)\end{matrix}$

for all i, 0≦i<C. In some systems, L may be equal to the number oftransmission “layers” used to transmit an information packet, thus L maybe directly referred to as the number of transmission layers. Forexample, for 3GPP LTE, when layer mapping for spatial multiplexing isused, up to 4 total number of transmission layers may exist, up to twotransport blocks may be sent in parallel, and the number of transmissionlayers for one transport block may be L=1 or L=2. For 3GPP LTE wherelayer mapping for transmit diversity is used, only one transport blockis sent over the multiple transmit antennas, and the number oftransmission layers for one transport block may be L=2 or L=4. Tocorrectly decode the information packet, the value of L may becommunicated on a control channel. For example, the value of L may bedetermined via a field in a control channel message, or by decoding thecontrol channel message and determining that a first message type ispresent instead of a potential second message type. Typical values of Lare 1, 2, and 4. Thus L is a variable in the physical channelsegmentation rule. While L is fixed for a given information packet, itmay change from packet to packet.

One approach to physical channel segmentation is to divide the Navailable modulation symbols approximately evenly among the code blocksegments. Since C may not divide N evenly, this is referred to here asan “equal-size” rule, the quotation marks denoting the approximatenature of the rule. Symbolically, assuming N is a multiple of L anddefining N_(L)=N/L, one possible equal-size rule is as follows:

$\begin{matrix}{M_{i} = \left\{ \begin{matrix}{{Q\; L\left\lceil \frac{N_{L}}{C} \right\rceil},} & {0 \leq i \leq {{N_{L}\mspace{14mu}{mod}\mspace{14mu} C} - 1}} \\{{Q\; L\left\lfloor \frac{N_{L}}{C} \right\rfloor},} & {{N_{L}\mspace{14mu}{mod}\mspace{14mu} C} \leq i \leq {C - 1}}\end{matrix} \right.} & (6)\end{matrix}$

Equation (6) can also be written using the variable γ=N_(L) mod C asfollows:

$\begin{matrix}{M_{i} = \left\{ \begin{matrix}{{Q\; L\left\lceil \frac{N_{L}}{C} \right\rceil},} & {0 \leq i \leq {\gamma - 1}} \\{{Q\; L\left\lfloor \frac{N_{L}}{C} \right\rfloor},} & {\gamma \leq i \leq {C - 1}}\end{matrix} \right.} & (7)\end{matrix}$

In equations (6) and (7), the rule assigns L extra modulation symbols toeach of the first γ code block segments compared to the remaining C-γcode block segments. In another embodiment, the same rule can assign anextra modulation symbol to each of the last γ code block segments. Thus,the following is another embodiment of the “equal-size” rule.

$\begin{matrix}{M_{i} = \left\{ \begin{matrix}{{Q\; L\left\lfloor \frac{N_{L}}{C} \right\rfloor},} & {0 \leq i \leq {C - \gamma - 1}} \\{{Q\; L\left\lceil \frac{N_{L}}{C} \right\rceil},} & {{C - \gamma} \leq i \leq {C - 1}}\end{matrix} \right.} & (8)\end{matrix}$

In another example, the γ code block segments with L extra modulationsymbols may not be adjacent to each other. Thus in one implementation ofthe “equal-size” rule, the rate matching entity, for example, entity 208in FIG. 2, is configured to determine, for γ encoded segments, a subsetof size M₀′ of encoded bits for each encoded segment. The rate matchingentity is also configured to determine, for C-γ encoded segments, asubset of size of M₁′ encoded bits for each encoded segment, wherein thesubset sizes M₀′ and M₁′ differ at most by P bits, where P is a productof a modulation order and a number of transmission layers used totransmit the transport block. Generally, M₀′ and M₁′ are determinedbased on a total number of bits G=QN available for transmission of thetransport block, wherein γ=G/(Q×L) mod C, where Q denotes the modulationorder and L denotes the number of transmission layers used to transmitthe transport block. In one embodiment, the subset sizes M₀′ and M₁′ areboth a multiple of the modulation order. In another embodiment, thesubset sizes M₀′ and M₁′ are both a multiple of the number oftransmission layers used to transmit the transport block. And in otherembodiment, the subset sizes M₀′ and M₁′ are both a multiple of theproduct of the modulation order and the number of transmission layersused to transmit the transport block. Thereafter, the selected subsetsof encoded bits are concatenated and then grouped to form modulationsymbols of the modulation order.

Note that these “equal-size” rules satisfy the requirements in bothEquations (4) and (5). Observe that with this rule, the code rate of thei-th segment, R_(i), is

$\begin{matrix}{R_{i} = \frac{K_{i}}{M_{i}}} & (9)\end{matrix}$

Thus, when the code block segments are sized differently, i.e., K_(i) isnot constant for all i, and/or the encoded bits sent over the physicalchannel varies, i.e., M_(i) is not constant for all i, the code rate mayvary among the segments. A large variation in code rate among the codeblock segments could be detrimental to the link packet error rate.

Alternatively, if a system uses approximately equal code block segmentsizes K_(i), and approximately equal physical channel sizes M_(i) shownin (6), then the code rates R_(i) are approximately, although notexactly, equal among the segments. In such a case, the “equal-size” ruleensures approximately equal link error rate among the code blocksegments, and consequently good link error rate for the entireinformation packet.

Thus in one implementation of the “equal-size” rule, after segmentingthe transport block into multiple segments and encoding each segment, asubset of encoded bits for each encoded segment is selected such that atleast two segments have different resultant coding rates. The selectionis based on a total number of bits G available for transmission of thetransport block. In one embodiment, the size of the selected subsets ofencoded bits for each encoded segment is a multiple of an order ofmodulation at which the selected subsets of encoded bits are modulated.In another embodiment, the size of the selected subsets of encoded bitsfor each encoded segment is a multiple of the number of transmissionlayers over which the transmission of the transport block occurs. And inyet another embodiment, the size of the selected subsets of encoded bitsfor each encoded segment is a multiple of the product of the modulationorder and the number of transmission layers over which the transmissionof the transport block occurs. Thereafter, the selected subsets ofencoded bits are concatenated and then grouped to form modulationsymbols of the modulation order.

Another approach to physical channel segmentation is to divide the Navailable modulation symbols in such a way that the code rate among allcode block segments is approximately equal. An “equal-rate” rule mayrectify performance problems introduced by an “equal-size” rule, but isnot as simple. Note that a solution that achieves an identical code rateacross all code blocks may not be possible.

One possible “equal-rate rule”, assuming N is a multiple of L, thatsatisfies both Equations (4) and (5) allots

$\begin{matrix}{M_{i} = \left\{ \begin{matrix}{{Q\;{L\left( {\left\lfloor \frac{K_{i}M_{*}}{K_{0}} \right\rfloor + 1} \right)}},} & {0 \leq i < D} \\{{Q\; L\left\lfloor \frac{K_{i}M_{*}}{K_{0}} \right\rfloor},} & {i \geq D}\end{matrix} \right.} & (10)\end{matrix}$

bits for segments 0≦i<C−1, where M_(*) is defined as

$\begin{matrix}{M_{*} = \left\lfloor \frac{N_{L}}{\left\lbrack {1 + {\sum\limits_{i = 1}^{C - 1}\left( {K_{i}/K_{0}} \right)}} \right\rbrack} \right\rfloor} & (11)\end{matrix}$

and the integer D is defined as

$\begin{matrix}{D = {N_{L} - {\sum\limits_{i = 0}^{C - 1}\left\lfloor \frac{M_{*}K_{i}}{K_{0}} \right\rfloor}}} & (12)\end{matrix}$

The transmitters disclosed herein and particularly the segmentation,padding, encoding, rate matching, concatenating, grouping and modulationentities thereof, are typically implemented by a firmware controlledprocessor or DSP. The complementary entities in the receiver may beimplemented similarly. Alternatively, these and other entities of thetransmitter and receiver may be implemented as hardware equivalentsand/or as a combination of hardware and software using discrete circuitsor as an application specific integrated circuit (ASIC).

While the present disclosure and the best modes thereof have beendescribed in a manner establishing possession by the inventors andenabling those of ordinary skill in the art to make and use the same, itwill be understood and appreciated that there are many equivalents tothe exemplary embodiments disclosed herein and that modifications andvariations may be made thereto without departing from the scope andspirit of the inventions, which are to be limited not by the exemplaryembodiments but by the appended claims.

What is claimed is:
 1. A wireless communication transmitter, comprising:a segmenting entity configured to segment a transport block into Csegments, an encoding entity configured to encode each segment into aset of encoded bits, a rate matching entity configured to determine, forγ encoded segments, a subset of size M₀′ of encoded bits for eachencoded segment, the rate matching entity configured to determine, forC−γ encoded segments, a subset of size M₁′ of encoded bits for eachencoded segment, the subset sizes M₀′ and M₁′ differ at most by P bits,where P is a product of a modulation order and a number of transmissionlayers for the transport block, a concatenating entity configured toconcatenate the selected subsets of encoded bits, and a grouping entityconfigured to group the concatenated selected subsets of encoded bits inorder to form modulation symbols of the modulation order.
 2. Thetransmitter of claim 1 further comprising a transmitter entityconfigured to transmit the modulation symbols over the number oftransmission layers.
 3. The transmitter of claim 1, wherein the subsetsizes M₀′ and M₁′ are both a multiple of the modulation order.
 4. Thetransmitter of claim 1, wherein the subset sizes M₀′ and M₁′ are both amultiple of the number of transmission layers.
 5. The transmitter ofclaim 1, wherein the subset sizes M₀′ and M₁′ are both a multiple of theproduct of the modulation order and the number of transmission layers.6. The transmitter of claim 1, M₀′ and M₁′ based on a total number ofbits G available for transmission of the transport block, whereinγ=G/(Q×L) mod C, where Q denotes the modulation order and L denotes thenumber of transmission layers.
 7. The transmitter of claim 6, whereinL=1, 2, or
 4. 8. The transmitter of claim 6, wherein Q=2, 4, or
 6. 9.The transmitter of claim 1, the segmenting entity configured to segmentthe transport block such that at least two segments contain a commonnumber of bits.
 10. A method in a wireless communication transmitter,the method comprising: segmenting a transport block into C segments;encoding each segment into a set of encoded bits; for γ encodedsegments, determining a subset of size M₀′ of encoded bits for eachencoded segment, for C−γ encoded segments, determining a subset of sizeM₁′ of encoded bits for each encoded segment, the subset sizes M₀′ andM₁′ differ at most by P bits, where P is a product of a modulation orderand a number of transmission layers for the transport block;concatenating the selected subsets of encoded bits; and grouping theconcatenated selected subsets of encoded bits in order to formmodulation symbols of the modulation order.
 11. The method of claim 10further comprising transmitting the modulation symbols over the numberof transmission layers.
 12. The method of claim 10, wherein the subsetsizes M₀′ and M₁′ are both selected to be a multiple of the modulationorder.
 13. The method of claim 10, wherein the subset sizes M₀′ and M₁′are both selected to be a multiple of the number of transmission layers.14. The method of claim 10, wherein the subset sizes M₀′ and M₁′ areboth selected to be a multiple of the product of the modulation orderand the number of transmission layers.
 15. The method of claim 10, thesubsets of sizes M₀′ and M₁′ are selected based on a total number ofbits G available for transmission of the transport block, whereinγ=G/(Q×L) mod C, where Q denotes the modulation order and L denotes thenumber of transmission layers.
 16. The method of claim 10, segmentingthe transport block such that at least two segments contain same numberof bits of the transport block.
 17. A method in a wireless communicationtransmitter, the method comprising: segmenting a transport block intomultiple segments; encoding each segment, each encoded segment having aset of encoded bits; selecting a subset of encoded bits for each encodedsegment such that at least two segments have different resultant codingrates, the selection based on a total number of bits available fortransmission of the transport block; concatenating the selected subsetsof encoded bits; and grouping the concatenated selected subsets ofencoded bits to form modulation symbols of the modulation order.
 18. Themethod of claim 17, wherein the size of the selected subsets of encodedbits for each encoded segment is a multiple of an order of modulation atwhich the selected subsets of encoded bits are modulated.
 19. The methodof claim 17, wherein the size of the selected subsets of encoded bitsfor each encoded segment is a multiple of the number of transmissionlayers over which the transmission of the transport block occurs. 20.The method of claim 17, wherein the size of the selected subsets ofencoded bits for each encoded segment is a multiple of the product ofthe modulation order and the number of transmission layers.